Pressurized skull crucible apparatus for crystal growth and related system and methods

ABSTRACT

The invention is directed to an apparatus, system and methods for growing high-purity crystals of substances that are peritectic at atmospheric pressure. The apparatus includes a pressure vessel that contains a pressurized gas. The apparatus also includes a cooling unit that is situated in the pressure vessel. The cooling unit receives a coolant flow from outside of the vessel, and has cooled surfaces that define an enclosure that receives the charge material. The apparatus further includes an inductive heating element situated in the vessel, that is coupled to receive electric power externally to the vessel. The element heats the interior portion of the charge material to form a molten interior portion contained by a relatively cool, exterior solid-phase portion of the charge material that is closer relative to the molten interior, to the cooled surfaces of the cooling unit. Because the exterior portion is the same material as the contained molten interior portion, few impurities are introduced to the molten interior portion of the charge material. Due to the pressure exerted by the gas contained in the vessel, the liquid interior of the charge material becomes congruently melting to prevent its peritectic decomposition. Therefore, crystals of substances that are peritectic at atmospheric pressure, can be produced from the liquid phase with the apparatus of this invention. In addition to electric power, the heating element receives a coolant flow from a feedthrough that extends through a wall of the pressure vessel. In proximity to the vessel wall, the feedthrough has two coaxial conductors to improve the electric power transfer to the heating element and to reduce heating of the external surfaces of the vessel. The two conductors of the feedthrough are cylindrical in shape, and define two channels for channeling a coolant flow to and from, respectively, the heating element. A shield formed of a cylindrical sheet of metal, for example, is positioned in the vessel to surround the heating element to focus energy emitted by the element to the charge material.

STATEMENT OF GOVERNMENT RIGHTS IN THE INVENTION

This invention was made pursuant to a Small Business Innovative Researchproject funded by the U.S. Government as represented by the Departmentof Army under Contract No. DAAH 04-94-C-0074 (Phase I). The U.S.Government has certain rights in the invention.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention is directed to an apparatus, system and methods forgrowing crystals of a substance from its liquid phase. The crystalsgrown in accordance with this invention have highly-ordered atomicstructures with few impurities or defects, and thus are suitable, forexample, for the production of wafer substrates used for the manufactureof semiconductor or optical devices or the like, or for the productionof superconductive materials.

2. Description of the Related Art

For decades, researchers have attempted to grow high-purity crystals ofsubstances that undergo peritectic reactions, from a melt. Theseattempts have proved unsuccessful, however, because substances thatbehave peritecticly, by their nature, decompose upon solidification fromthe liquid phase into non-stoichiometric compositions from which acrystal cannot be grown without significant lattice defects due to localvariations of the quantities of the various elements and/or compoundsthat compose the substance. The difficulties of growing crystals ofperitectic substances from a melt have been widely recognized. Forexample, one researcher has noted that the ". . . freezing of aperitectic reaction (or compound), to complete equilibrium, ispractically impossible to attain." W. J. Boettinger, MettalurgicalTransactions Vol. 5, pg. 2023, published 1974. Another commentator notedthat researchers are exhibiting "a very lively interest" in peritecticreactions, but the ability to control these reactions has alluded many.D. H. St. John, L. M. Hogan, Acta Metallurgica Vol. 25, pg. 77,published 1977. Even more recently, a textbook indicates that manysubstances decompose peritecticly when melted into a non-stoichiometricliquid with an indeterminate ratio of components or elements. James F.Shackleford, Introduction to Materials Science for Engineers, MacmillanPublishing Company, New York, Third Edition, pg. 222, published 1992.Similar observations regarding the freezing of substances that undergoperitectic reactions have been made in a number of publications. See,for example, J. P. Schaffer, A. Saxena, S. D. Antolovich, T. H. Sanders,Jr., S. B. Warner, The Science and Design of Engineering Materials,Richard D. Irwin, 1995, pp. 274-76; R. Glardon, W. Kurz, Journal ofCrystal Growth 51, 283, published 1981; M. Hillert, Solidification andCasting of Metals, The Metal Society, London, published 1979; D. H. St.John, L. M. Hogan, Acta Metallurgica 35, 171, published 1987; F. N.Rhines, Phase Diagrams in Metallurgy, McGraw Hill, New York, 1956, pp.85-88.

FIG. 1 is a phase diagram explaining the behavior of a substance whichundergoes a peritectic reaction as the substance is cooled at constantpressure and volume from the liquid- or gas- to the solid-phase. As usedin this document, a peritectic (or synonymously, a `peritectic-type`reaction) is defined as a reaction ". . . in which one phase decomposeswith rising temperature into two new phases." Frederick N. Rhines, PhaseDiagrams in Metallurgy: Their Development and Application, McGraw-HillBook Company, New York, Pg. 83, published 1956. Thus, although somescientists in this field refer to a `peritectic reaction` as one inwhich a solid decomposes with rising temperature into a solid and aliquid, the term `peritectic` as used in this document consistent withRhines' definition, refers to decomposition with rising temperature fromany one phase into any two phases. The substance of FIG. 1 includescomponents A and B that can be elements or compounds, contained within aspecific volume at a specific pressure. With substances that containmore than two components, many different phases are possible, so thesubstance in FIG. 1 is a relatively simple example provided for ease inillustrating a substance that undergoes a peritectic reaction.

At the start temperature, the peritectic substance is in the liquid orgas phase with a composition AB, where A and B denote respectiveproportions of the element(s) or compound(s) that comprise theperitectic substance. As the substance cools to the peritectictemperature T_(P), the element or compound B begins to precipitate as asolid out of the liquid or gas phase, causing the remaining liquid orgas to become relatively rich in A and depleted in B. As more heat isextracted from the liquid substance, the B component of the peritecticsubstance continues to precipitate or sublimate out of the liquid or gasphase until the proportion of A to B reaches a composition A'B'determined by the shape of the phase boundary. At this point, as furtherheat is extracted from the substance, the remaining liquid or gas willprecipitate or sublimate to form a solid composition A'B' that is richerin A and depleted in B relative to the initial composition AB.

From FIG. 1, the problem presented when attempting to solidify asubstance which undergoes a peritectic reaction can be readilyunderstood. Assuming that the initial composition AB was selected with astoichiometric proportion of A to B, the behavior of the composition asheat is extracted from the system results in the initial formation ofcomponent B and the eventual formation of the non-stoichiometriccomposition A'B'. The resulting solid phase will therefore containinclusions of B in a matrix of composition A'B', which is extremelyunlikely to have the same physical and/or chemical properties as thedesired compound AB.

There are many crystalline substances which undergo a peritecticreaction at atmospheric pressure, that are significantly important (orhave significant promise of being important) for use in a wide varietyof industries. For example, substances such as aluminum nitride (AlN),silicon carbide (SiC), gallium nitride (GaN), yttrium barium cupricoxide (YBa₂ Cu₃ O_(x)) and aluminum gallium nitride (AlGaN_(x)) areknown or believed to have significant uses for a wide variety ofsemiconductor, optical or superconductor applications, if available inhighly pure crystalline form. With respect to gallium nitride (GaN), onewriter has commented that "gallium nitride substrates are the great hopeof the nitride community . . . ", and that ". . . good results obtainedwith nitride light-emitting diodes! would be immediately pushed forwardin one large step if high quality gallium nitride substrates were tobecome available." G. W. Wicks, Growing Interest in Nitrides, CompoundSemiconductor, v.2, n.1, pg. 42, January-February 1996. However, due tothe extremely slow production rates (typically on the order of micronsper hour) at which these peritecticly-behaving substances can beproduced using vapor growth techniques, these substances are relativelyscarce and expensive. Therefore, the benefits derived through the use ofthese high-purity, crystalline substances, have been greatly limited bythe general unavailability of these substances at reasonable cost.Accordingly, there is a strong need for a device or technique forrapidly growing high-purity, crystalline substances that undergoperitectic reactions if they are attempted to be grown with conventionaldevices or techniques.

Another problem related to this invention involves safety concerns posedby many crystal-growing devices. More specifically, the furnace chambersurfaces of a crystal-growing device are heated to extremely hightemperatures, and pressurized to relatively high pressures, to grow manykinds of substances in vapor phase processes. If the external surfacesof the furnace chamber are not cooled, these heated surfaces can becomeweakened and rupture under the pressure of the gas contained in thefurnace chamber, thus presenting a significant risk of injury to personsin a work environment by explosion of the furnace. To reduce the dangerof injury, cooling equipment has been used to cool the furnace chambersurfaces of a crystal-growing device. However, the cooling equipmentsystem generally adds significant expense and complexity to thecrystal-growing device. It would therefore be desirable to provide acrystal-growing apparatus that operates with relatively cool externalsurfaces, but which does not require additional cooling equipment andthe expense and complexity associated therewith.

Still another problem related to this invention pertains to energyconsumption required in previously known crystal-growing devices.Specifically, in order to produce the extremely high temperatures neededto melt a charge material used to grow a crystal, the typicalcrystal-growing device consumes considerable power. The powerconsumption problem of the typical crystal-growing device is exacerbatedby the fact that these devices often must be operated continuously forseveral hours or even days to produce a single crystal. Therefore, thepower consumed in previously known crystal-growing devices has addedsignificantly to the cost of producing crystals with typicalcrystal-growing devices. It would be extremely desirable to reduce theamount of power required to produce a crystal.

SUMMARY OF THE INVENTION

This invention overcomes the above-noted disadvantages. In accordancewith this invention, an apparatus for growing a crystal from a chargematerial in its liquid phase, includes a pressure vessel for containinga pressurized gas. The apparatus also includes a cooling unit forsituation in the pressure vessel, that has cooled surfaces that definean enclosure to receive the charge material. The enclosure's cooledsurfaces are partially opened to expose the charge material to pressureexerted by the gas contained in the pressure vessel. The apparatusfurther includes an induction heating element for situation in thepressure vessel, that heats an interior portion of the charge materialto a molten, liquid state. The charge material's molten interior portionis contained by a relatively cool, exterior portion of the chargematerial that remains in the solid phase despite the heat generated bythe heating element, due to its closer situation relative to the molteninterior portion, to the cooled surfaces of the cooling unit. Thus, thesolid, exterior portion of the charge material, referred to as a`skull`, acts as a crucible that contains the molten interior portion ofthe charge material. The charge material's molten interior portion canbe cooled to form a crystal by reducing the amount of heat generated bythe heating element, or by moving the heating element relative to thecharge material so that formerly molten portions of the charge materialbecome solidified. Importantly, the gas pressure in the vessel rendersthe charge material congruently melting even if the charge material is asubstance that peritecticly decomposes upon solidification atatmospheric pressure. Thus, the apparatus of this invention can rapidlyproduce high-purity crystals of substances that undergo peritecticreactions at atmospheric pressures.

The apparatus of this invention can also include a shield situated inthe pressure vessel and arranged to surround the heating element andcharge material. The shield reflects and focuses energy emitted by theheating element to the charge material, for more efficient use of theenergy to heat the charge material's interior portion to a molten state.The shield also prevents heating of the pressure vessel wall atlocations in close proximity to the heating element. The shield ispreferably composed of a material with a relatively high electricalconductivity such as copper or other suitable metal.

Also, the apparatus can include a feedthrough extending through the wallof the pressure vessel, that serves to supply electric power and coolantfrom outside of the pressure vessel, to the heating element that issituated inside the pressure vessel during operation of the apparatus.Preferably, the feedthrough includes a first elongated electricconductor with an inner wall that defines a conduit for channeling acoolant flow, and a second elongated electric conductor enclosing aportion of the first conductor at least in a region in which thefeedthrough extends through the vessel wall. This approximately coaxialarrangement of the first and second conductors results in relativelyefficient electric power transfer to the heating element for use inheating the charge material. In the feedthrough, a second conduit isdefined between the outer wall of the first conductor and the inner wallof the second conductor. Inside of the pressure vessel, the conduits arecoupled to supply and discharge a flow of coolant to the heatingelement, and the first and second conductors are electrically coupled tosupply electric power to the heating element. Outside of the pressurevessel, the first and second conductors can be coupled to receiveelectric power from a generator, for example, and the first and secondconduits are respectively coupled to receive and discharge the coolantflow, or vice versa, in a circulatory or non-circulatory manner. If thecoolant is a conductive substance such as water, the feedthroughpreferably includes an electrical insulator arranged to surround andcontact the outer wall of the first conductor, that electricallyinsulates the first and second conductors from one another. If theelectrical insulator is used, the second conduit is defined between anouter wall of the electrical insulator and an inner wall of the secondconductor. The aforementioned shield can be electrically coupled to thesecond conductor that is used as an electrical ground, to increase theenergy-focusing effect of the shield.

Further, the apparatus can include an actuator for moving the coolingunit relative to the heating element, so that the molten zone traversesan axis of the charge material to form an elongated crystal. In thepreferred embodiment, the actuator includes a hydraulic device such as ahydraulic piston, that extends or retracts based on a hydraulic fluidflow. The hydraulic device is preferably coupled between the coolingunit and an inner wall of the pressure vessel. To prepare for acrystal-growing operation, the actuator preferably includes a hydraulicpump that can be activated to drive hydraulic fluid into the hydraulicdevice, causing the device to extend and move the cooling unit to afirst position relative to the heating element. The actuator preferablyincludes a valve coupled between and communicating with the hydraulicdevice and pump. In the crystal-growing mode of operation, the valve canbe set to a predetermined flow rate. Due to the weight of the coolingunit and the charge material situated therein, hydraulic fluid is forcedout of the device at a rate determined by the valve setting. Therefore,the valve setting controls the crystal growth rate.

A system in accordance with this invention is similar to theabove-described apparatus, but additionally includes the charge materialthat can be a substance that is peritectic at atmospheric pressure, suchas gallium nitride (GaN), aluminum nitride (AlN), silicon carbide (SiC),yttrium barium cupric oxide (YBa₂ Cu₃ O_(x)) and aluminum galliumnitride (AlGaN_(x)).

Advantageously, with the apparatus and system of this invention, acrystal of a substance that is peritectic at atmospheric pressure, canbe made to be a congruently-melting substance due to pressurization byan appropriate gas contained in the pressure vessel, that prevents thesubstance from decomposing by peritectic reaction when growing a crystalfrom the charge material in its liquid phase. Therefore, through gaspressurization, stoichiometry of the molten charge material can bemaintained during solidification of the charge material so that thecrystal grown with the apparatus has relatively few lattice defects.Additionally, because the crystal is grown from the liquid phase, thegrowth of the crystal can be performed with relative rapidity. Also,because the molten interior charge material is composed of the samesubstance as the cooled exterior skull portion of the charge material,relatively few impurities are introduced into the crystal grown with theapparatus of this invention. Further, the energy-focusing capability ofthe shield helps to prevent heating of the external surfaces of thevessel, while reducing power consumption by focusing the energy emittedby the heating element to the charge material. The feedthrough alsoachieves increased energy efficiency relative to conventionalcrystal-growing devices through the coaxial arrangement of itsconductors that are coupled to supply electric power to the heatingelement. Also, because the feedthrough defines two conduits forchanneling a coolant flow to and from the heating element, thefeedthrough is cooled effectively so that the external surfaces of thepressure vessel in the vicinity of the feedthrough, are not heated totemperatures that would weaken the feedthrough or pressure vessel wallto the point of presenting a significant risk of explosion.

A first method in accordance with this invention includes steps ofcontaining a molten liquid portion of a charge material, in a skullcomposed of a solid portion of the charge material, and a step ofpressurizing at least the molten liquid portion of the charge materialwith a gas during the performance of the containing step. Preferably,the method also includes a step of cooling the molten liquid portion ofthe charge material to solidify the charge material to form a crystal,during the performance of the pressurizing step. Advantageously, throughthe use of the pressurizing step, a substance that undergoes aperitectic reaction at atmospheric pressure can be made to becongruently-melting to prevent decomposition during crystal growth.Accordingly, a crystal with proper stoichiometry, and hence relativelyfew crystalline lattice defects, can be produced from the substance inits liquid phase. Also, because the containing step uses a solid skullcomposed of the same substance as the molten charge material for thecontainment thereof, relatively few impurities are introduced to thecrystal. Further, by performing the preferred cooling step together withthe pressurizing step, peritectic decomposition of the charge materialis prevented during cooling so that the molten charge material cools toa solid crystalline form with few lattice defects.

A second method in accordance with this invention includes a step ofheating an interior portion of a charge material body to melt theinterior portion, and a step of cooling an exterior portion of thecharge material body so that the exterior portion is in a solid phaseand contains the molten interior portion during the performance of theheating step. The second method also includes a step of pressurizing thecharge material body with a gas during performance of the heating andcooling steps. Preferably, the second method also includes a step ofcooling the molten interior portion of the charge material body to forma solid-phase crystal of the charge material. Also preferred, theheating step can be performed in a limited area along an axis of thecharge material body, and the second method can include a step of movingthe heat source in a direction along the axis of the material body sothat a step of cooling of the interior portion of the charge materialbody occurs in regions previously heated by the heat source as the heatsource moves along the axis of the charge material body.

Advantageously, the heating of the interior portion of the chargematerial body while cooling the exterior portion of the body, provides aliquid phase molten interior portion that is contained by a cooler,solid phase exterior portion of the same charge material. Thus, theexterior portion of the charge material does not introduce significantamounts of impurities into the molten interior portion of the chargematerial body. The pressurizing step prevents the interior portion ofthe charge material from undergoing peritectic decomposition uponsolidification so that the second method can be used to manufacturecrystals of substances that undergo peritectic reactions at atmosphericpressure. Further, the step of moving the heat source along the axis ofthe charge material body allows an elongated crystal to be formed sothat relatively large crystals, and hence a greater quantity of usefulmaterial, can be produced by the apparatus.

These together with other objects and advantages, which will becomesubsequently apparent, reside in the details of construction andoperation as more fully hereinafter described and claimed, referencebeing made to the accompanying drawings, forming a part hereof, whereinlike numerals refer to like parts throughout the several views.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a phase diagram of a substance that undergoes a peritecticreaction;

FIGS. 2A, 2B, 2C, 2D and 2E are cross-sectional views of an apparatusand system in accordance with this invention; and

FIG. 3 is a relatively detailed view of an electric power generator foruse with the apparatus and system of this invention; and

FIG. 4 is a cross-sectional view of a feedthrough in accordance withthis invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In FIG. 2A, an apparatus 1 in accordance with this invention includes apressure vessel 2 that encloses a space in which a crystal is grown.Preferably, the pressure vessel 2 includes a chamber member 3 that isroughly bell-shaped, having a dome-like upper end in FIG. 1, anelongated cylindrical side wall and an outwardly extending flange 4 atits open lower end in FIG. 1. Preferably, the chamber member 3 hasrelatively thick steel walls (about two inches in thickness, forexample) that can withstand relatively high-pressures.

To enclose the open end of the pressure vessel 2, a plate member 5 has adisc-like shape and preferably is made of steel with a thickness ofseveral inches. The plate member 5 also defines several centralapertures to receive various elements of the apparatus yet to bedescribed in detail. At intervals about their respective circumferences,the flanges 4, 6 have corresponding apertures to receive bolts 7 thatare threaded at both of their ends. The threaded ends of the boltsreceive respective nuts 8. To form a pressure-tight seal between thechamber member 3 and the plate member 6, a gasket 9 is positionedbetween the flanges 4, 6 before joining the flanges together andtightening the nuts 8. Preferably, the gasket 9 is a Chevron®- typegasket that is capable of maintaining a pressure-tight seal under therelatively high pressures experienced by the pressure vessel 2.

A conduit 10 extends through an aperture in the plate member 5, and hasa first end that communicates with the space enclosed by the pressurevessel 2 when the vessel is assembled. Preferably, the conduit 10, likethe other conduits of the apparatus 1 yet to be described, is composedof a length of a pipe made of a metal such as copper, although othertypes of conduits can be useful if they are sufficiently durable towithstand the relatively high temperatures and pressures existing in thevessel 2 during operation and damage by accidental contact. A fitting 11is coupled to the conduit 10 and the plate member 5 to form apressure-tight seal therebetween. Preferably, the fitting 11 (like theother fittings used in the apparatus that have not yet been described)is a metal compression type fitting, although other fitting types,including O-ring varieties, can be used effectively. In FIG. 2B, asecond end of the conduit 10 is coupled to communicate with a first endof a hose 12 that, like other hoses used in the apparatus, is preferablycomposed of a high-pressure and high-temperature plastic material.Preferably, the hose 12 is secured in place with a hose clamp (notshown) or other suitable device. In the following description, forsimplicity, specific reference to a hose clamp or other device used tosecure a hose to another element, will be omitted. However, it should beunderstood that such hose clamps are preferably used at each junction ofa hose with another element throughout the apparatus 1.

A second end of the hose 12 is coupled to communicate with one leg of afour-way conduit 13 that is a commercially-available device. Oppositethe leg coupled to the second end of the hose 12, the four-way conduit13 includes three valved legs. The three valved legs can each beselectively opened or closed by appropriate manipulation of one of thevalves 14, 15, 16 associated with each leg. The leg with the valve 14,is coupled to communicate with a first end of a hose 17 that has asecond end coupled in communication with a vacuum unit 18. The vacuumunit 18 can be a pump or other commercially-available device suitable todevelop a suction to draw gas from the hose 17 when the unit 18 isactivated. The leg of the four-way conduit 13 with the valve 15 iscoupled to communicate with a first end of hose 19 that has a second endcoupled in communication with a pressurized gas unit 20. The unit 20supplies pressurized gas to the hose 19. Preferably, the unit 20includes a pressurized gas tank 21. The tank 21 contains a gas of a typethat is appropriate to supply the pressure needed to prevent a substancefrom peritecticly decomposing upon solidification so that a crystal ofthe substance can be grown in the apparatus 1. The pressurized gas unit20 also preferably includes a valve 22 that can be controlled by hand orby an external electric signal, for example, depending upon the type ofvalve, to determine the pressure of the gas supplied by the unit 20. Thefour-way conduit 14 also includes a leg with a valve 16 that can be usedto bleed pressurized gas from the vessel before opening the vessel 2.

The apparatus 1 also includes a cooling unit 23 (see FIG. 2A) thatfunctions to cool an exterior portion 24 of a substance 25 from which acrystal 26 is made. The substance 25 is often referred to as a `chargematerial.` The exterior portion of the charge material is cooled by theunit 23 to a temperature sufficiently low to maintain its solid phase.Thus, the exterior portion of the charge material acts as a crucible tocontain a molten interior portion 27 of the charge material. Because thesolid exterior portion contains the liquid interior portion of thecharge material 25, the solid exterior portion of the charge material issometimes referred to as a `skull.` Due to the fact that the molteninterior portion 27 and the solid exterior portion 24 (i.e., the skullcrucible) are made of the same charge material 26, relatively fewimpurities are introduced into the interior portion 27 relative tocrystal-growing device, that use a crucible of a different material thatwill react at least to some extent with the molten material containedtherein. As often occurs when growing a crystal, a pocket of gas 28 maydevelop above the molten interior portion 27.

The cooling unit 23 preferably includes a manifold 29 having a surface30 upon which are mounted a plurality of elongated cooling members 31, aconfiguration similar to the apparatus shown in FIG. 2 of U.S. Pat. No.4,224,100 issued Sep. 23, 1980 to Robert A. Hartzell, that isincorporated herein by reference. Preferably, the members 31 arecircularly arranged about a longitudinal axis of the cooling unit 23(that is parallel to the vertical direction in FIG. 4) to define innerside cooled surfaces of an enclosure 32 that has a closed floor definedby the manifold's surface 30. The enclosure 32 thus contains the chargematerial 25, and cools the exterior portion of the charge material tomaintain its solid phase. The manifold 29 defines input and outputpassages (not shown) in its interior, and the input and output passagesare coupled to respective input and output conduits of the members 31.The members 31 essentially include two concentric inner and outer tubesconfigured so that the inner tube has an open end toward the endextremity of the member 31, and so that the outer tube has a greaterlength than the inner tube that is sealed at its end for containment ofthe coolant flowing therein. The coolant flow that is incoming to themember 31 from the input passage of the manifold 29, flows verticallyupward in FIG. 1 through the inner tube, and flows downward in FIG. 1between the inner and outer tubes, for return to the outer passages ofthe manifold 29, or vice versa. Preferably, the manifold 29 and themembers 31 are made of a material that has a relatively high thermalconductivity and durability, such as copper or other suitable metal.

To prevent the charge material 25 from erupting outward to damage orfoul elements of the apparatus 1, the members 31 can be enclosed by aprotective cylinder 33, preferably made of a ceramic material, that fitsin sleeve fashion over the members 31 and is held in position thereby.

The input and output passages of the manifold 29 are coupled tocommunicate with respective ends of conduits 34, 35. The conduits 34, 35are flexible, and can be made of relatively thin copper tubing or thelike. The ends of the conduits 34, 35 opposite the ends coupled to themanifold 29, are coupled to communicate with respective ends of conduits36, 37 that are preferably made of relatively thick, sturdy coppertubing. The ends of the conduits 34, 35 are preferably coupled torespective ends of the conduits 36, 37 by welding or the like. Theconduits 36, 37 extend through respective apertures defined in the platemember 5. Fittings 38, 39 are coupled between respective conduits 36, 37and the plate member 5 to form pressure-tight seals between the platemember 5 and the conduits 36, 37. The ends of the conduits 36, 37opposite the ends coupled to the conduits 34, 35, are coupled tocommunicate with respective first ends of hoses 40, 41 (see FIG. 2C)that have second ends coupled to receive and discharge, respectively, aflow of coolant from and to a coolant supply unit 42.

Preferably, the coolant supply unit 42 includes an orifice 43 thatdefines a constriction in the coolant flow path that causes pressurebuild-up in the hose 41, the conduits 37, 35 and hence, in the coolingunit 23. The pressurization of the coolant prevents its vaporizationunder the heat emanating from the charge material 25 so that the coolantcan effectively transfer heat away from the cooling unit 23 to avoiddamage or destruction thereof, and to ensure that the exterior portion24 of the charge material 25 remains in the solid phase.

The orifice 43 has an end opposite that receives the coolant from thehose 41, that is coupled to communicate with a diverter 44 in the unit42. The diverter 44 is a commercially available device that can be setmanually, for example, to couple the flow from the orifice 43 to eitherthe hose 45 or the hose 46 of the unit 42. In normal operation of theapparatus, it is preferred to set the diverter 44 to direct the flowfrom the orifice 43 to the hose 45. The hose 45 channels the flow ofcoolant received from the diverter 44 to the coolant tank 47 of the unit42, for holding a relatively large volume of the coolant 48. Preferably,the tank 47 holds between fifty and one-hundred gallons the coolant 48.The coolant tank 47 is coupled to communicate with an input of coolantpump 49 of the unit 42, that provides the motive force to circulate thecoolant 48 through the cooling unit 23. The coolant pump 49 can be oneof a wide variety of commercially available pumps. The output of thepump 49 is coupled to communicate with an end of a hose 50 of the unit42, whose opposite end is coupled to communicate with a diverter 51 ofthe unit 42. The diverter 51 is also coupled to communicate with an endof the hose 52 of the unit 42. The diverter 51 can be selectivelycontrolled to receive the coolant flow from the hose 50 or to receive acoolant flow from a water tap supply via the hose 52 of the unit 42. Innormal operation, the diverter 51 preferably couples the hose 50 intocommunication with the hose 40.

The coolant supply unit 42 also includes a refrigeration unit 53, a hose54, a coil 55 and a hose 56 in which a coolant 57 flows. Therefrigeration unit 53 is coupled to communicate with an end of the hose54 whose opposite end is coupled to the coil 55. The coil 55 is situatedinside of the tank 47, and is coiled to increase the area available forheat-transfer from the coolant 48 to the coil 55. Also preferred, thecoil 55 is composed of a material with a high thermal conductivity suchas copper. The coil 55 has a second end that is coupled to communicatewith a the hose 56 whose opposite end is coupled to the refrigerationunit 53.

The refrigeration unit 53 serves to cool the coolant 57, and includes apump (not shown) that provides the motive force to drive the coolant 57through the hose 54, the coil 55 and the hose 56 for return to the unit53. In normal operation of the coolant supply unit 42, the coolant 48 inthe tank 47 is cooled by heat-transfer to the coolant 57 circulating inthe coil 55. Preferably, the coolants 48, 57 are water with an additivesuch as automotive antifreeze (i.e., ethylene glycol), that has arelatively high vaporization temperature. However, the ethylene glycoladditive should not be added in an amount greater than ten percentbecause it has a relatively low heat capacity.

The coolant supply unit 42 is part of a circulatory cooling system,meaning that a fixed amount of coolant is circulated continuously tocool the cooling unit 23. However, particularly in emergency situationssuch as failure of the coolant pump 49 or the refrigeration unit 53, anon-circulatory system can be implemented in the apparatus 1 withoutdeparting from the scope of this invention. Specifically, the diverter51 of the coolant supply unit 42 can be switched to receive a flow oftap water from the hose 52, that is circulated through the cooling unit23. The return flow from the cooling unit 23 can be coupled to the hose46 by appropriately setting the diverter 44, so that the heated coolantis directed to a drain for disposal. However, a circulatory coolingsystem is preferred over the non-circulatory cooling system because thedisposal of the significant amounts of coolant needed to cool thecooling unit 23 adds significant expense to the operational cost of theapparatus, particularly considering that, despite its comparativelyrapid crystal growth rate, the apparatus 1 can require several hours ofoperation to produce a crystal from the charge material.

An inductive heating element 60 is situated in the pressure vessel 2 atleast in operation of the apparatus and system of FIGS. 2A, 2B, 2C, 2Dand 2E. The element 60 includes a coil 61 that encircles the coolingunit 23 about an axis thereof (i.e., the vertical axis in FIG. 2A). Thecoil 61 can be a coiled metal tube composed of copper, for example. Theends of the coil 61 are coupled electrically to conductors 62, 63, andare coupled to communicate with conduits defined by the conductors 62,63. The conductors 62, 63 are elements included in a feedthrough 64 thatfunctions to supply an alternating electric current to the inductiveheating element 60 to heat the charge material 25, and to supply anddischarge a coolant flow circulated through the coil 61 to preventoverheating of the element 60. The feedthrough 64 extends through theplate member 5 of the pressure vessel 2, and is secured to the platemember 5 by a fitting 65 that forms a pressure-tight seal between theplate member 5 and the feedthrough 64.

At the end of the feedthrough 64 situated outside of the pressure vessel2, the conductors 62, 63 are electrically coupled to an electric powergenerator 66 (see FIG. 2D). The generator 66 can be any of a widevariety of commercially available electric power generators as will bereadily understood by those of ordinary skill in this technical field.The generator 66 is commercially available by specification of a desiredrange of electric power frequencies appropriate to melt the particulartype of material 25 from which a crystal 26 is to be made. The electricpower generator 66 generates an alternating electric current, atfrequencies up to the radio frequency (rf) range or even beyond, that issupplied to the inductive heating element 60. More specifically, thegenerator 66 generates electric power that is supplied to the conductors62, 63 of the feedthrough 64, and to the coil 61 of the inductiveheating element 60, to produce the electromagnetic field that heats thecharge material 25. Preferably, the conductor 63 is electrically coupledto the ground terminal of the generator 66 as well as to the platemember 5 so that the entire pressure vessel 2 is electrically grounded.The conductor 62 is coupled to the high-voltage terminal of thegenerator 66. The conductor 62 is preferably insulated in thefeedthrough 64 from the plate member 5 of the pressure vessel(particularly if a non-electrically insulating coolant flows in theconduits defined by the conductors 62, 63) to prevent the occurrence ofa short circuit with attendant danger to a person or the apparatusitself.

In FIG. 2D, the conduit defined by the conductor 63 is coupled toreceive a flow of coolant from a coolant supply unit 70 for circulationthrough the heating element 60. The return flow from the heating element60 flows through the electric power generator 66 to cool components ofthe generator 66. From the power generator 66, the coolant flows to thecoolant supply unit 70 for cooling and, in the preferred operation ofthe apparatus 1, recirculation through the heating element 60 and theelectric power generator 66.

The coolant supply unit 70 includes a diverter 71 coupled to receive thecoolant flowing from the generator 66 through the conductor 62. Thediverter 71 is coupled to communicate with hoses 72, 73, and can be setto couple the conductor 62 in communication with either the hose 72 orthe hose 73 of the unit 70.

In normal operation, the diverter 71 is set to couple the conductor 62into communication with the hose 72 so that the coolant flows to acoolant tank 74 of the unit 70. The coolant tank 74 holds a relativelylarge supply of the coolant 75, and preferably has a capacity of fiftyto one-hundred gallons. The tank 74 is coupled in communication with aninput of the coolant pump 76 of the unit 70, that provides the motiveforce to drive the coolant 75 through the electric power generator 66and the heating element 60. The pump 76 can be one of a wide variety ofcommercially-available pumps. An output of the coolant pump 76communicates with an end of the hose 77 of the unit 70, whose oppositeend is coupled to communicate with one input to a diverter 78 of theunit 70. The diverter 78 has another input coupled to communicate withan end of a hose 79 of the unit 70, whose opposite end is coupled to atap water supply. In normal operation, the diverter 78 is set to couplethe hose 77 to the conductor 63 so that the coolant flows from thecoolant pump 76, through the heating element 60, through the generator66 and back to the coolant supply unit 70 for recirculation.

To cool the coolant 75, the coolant supply unit 70 preferably includes arefrigeration unit 80, a hose 81, a coil 82 and a hose 83. Therefrigeration unit 80 is coupled to communicate with a first end of thehose 81 whose opposite end is coupled to communicate with an end of thecoil 82. The opposite end of the coil 82 is coupled to communicate withan end of the hose 83 that has an opposite end coupled to communicatewith the unit 80. The refrigeration unit 80 can be one of a wide varietyof commercially-available devices, and serves to cool a coolant 84. Theunit 80 includes a pump (not shown) that drives the refrigerated coolant84 through the hose 81 to the coil 82. The coil 82 is situated in thetank 74 and spirals in the coolant 75 to increase the area available forheat transfer from the coolant 75, to the coolant 84 flowing in the coil82. Preferably, the coil 82 is composed of a material such as copper,that has a high thermal conductivity. The coolant 84 with an elevatedtemperature due to heat transfer from the coolant 75, flows to the hose83 for return to the refrigeration unit 80 for recooling. Preferably,the coolant 84, like the coolant 75, is a liquid substance such as waterwith an additive, for example, ethylene glycol, to increase thevaporization temperature of the substance. The ethylene glycol additiveis preferably restricted in amount to about ten percent or less becauseit has a relatively low heat capacity.

The coolant supply unit 70 is normally a circulatory coolant system.However, particularly in emergency situations, the coolant supply unit70 can be converted into a non-circulatory system by switching thediverter 78 to receive the tap water flow from hose 79, and by switchingthe diverter 71 to direct the tap water coolant to the drain fordisposal. Thus, in the event of a malfunction such as a coolant pump orrefrigeration unit failure, the coolant supply unit 70 can rapidly bechanged to a configuration that uses tap water to cool the electricpower generator 66 and the heating element 60. In general, thisnon-circulatory system is not preferred because, over the several hourstypically necessary to complete a crystal-growing operation, the amountof tap water used can be a significant source of expense in operatingthe apparatus. Nonetheless, the non-circulatory system is an option thatcan be used with the apparatus 1 of this invention.

In FIG. 2A, to focus the energy emitted by the inductive heating element60, a shield 85 in accordance with this invention, is preferably used.The shield 85 is composed of a metal cylinder made of copper or otherhigh electrical conductivity material, and is situated in the pressurevessel 2 to surround at least the coil 61 of the heating element 60. Theshield 85 also serves to reduce heating of the wall of the chambermember 3 that is situated in proximity to the heating element 60, afeature of this invention that prevents thermal weakening of the chambermember's wall with the attendant danger of explosion by sudden releaseof the pressurized gas due to rupture of the wall. To support the shield85 in position relative to the inductive heating element 60, the shield85 can be seated on a shield support member 86 that rests on the platemember 5. The support member 86 can be a cylindrical section of plasticpipe, for example, such as a polyvinyl chloride or othercommercially-available plastic pipe. Alternatively, brackets 87 mountedbetween the wall of the chamber member 3 and the shield 85, can be usedto support the shield 85 in the appropriate position to surround theheating element 60. Preferably, a conductor 88 such as a length ofcopper wire, is electrically coupled between the shield 85 and theconductor 88 to electrically ground the shield 85. Preferably, an end ofthe conductor 88 is attached by welding to the shield 85, and itsopposite end is welded or wrapped several times about the conductor 63where it comprises the outer surface of the feedthrough 64.

It is believed that the beneficial behavior of the shield 85 is due toits reflection of the rf radiation from the heating element 60.Accordingly, to maximize its beneficial radiation-focusing effects, theshield 85 is preferred for use with the heating element 60 operating atradiation frequencies (rf, for example) at which the shield 85 isreflective to the radiation.

To increase the size of the crystal 26 produced with the apparatus 1, itis desirable to move the heating element 60 relative to the cooling unit23. When so moved, a limited area in which the charge material 25 issufficiently heated to form the molten interior portion 27, moves alongthe axis (specifically, the vertical axis in FIG. 2A) of the chargematerial 25 to progressively heat and liquefy the charge material 25 toproduce the molten interior portion 27. As the limited area heated bythe heating element 60 moves along the axis, the previously moltenportion of the charge material 25 crystallizes. The resulting crystal 26is elongated along the vertical axis in FIG. 2A.

To affect the movement of the heating element 60 relative to the coolingunit 23, an actuator 90 in accordance with this invention, is used. Theactuator 90 includes a hydraulic device 91 that is coupled between thecooling unit 23 and the plate member 5. The hydraulic device 91 can beselectively extended or retracted by supplying or extracting hydraulicfluid from the hydraulic device 91. For example, the device 91 can beone of several commercially-available devices including a device thathas a cylinder and a piston that moves in the cylinder based on the flowof hydraulic fluid to or from the device. The actuator 90 includes aconduit 92 that has a first end coupled to supply or extract hydraulicfluid from the device 91. The conduit 92 is secured to the plate member5 with a fitting 93 of the actuator 90, that forms a pressure-tight sealbetween the conduit 92 and the plate member 5. As so fixed by thefitting 93, the conduit 92 extends through the plate member 5, and has asecond end situated outside of the pressure vessel 2. To the second endof the conduit 92 (see FIG. 2E), a first end of a hose 94 of theactuator 90, is coupled in communication. The actuator 90 also includesa valve 95. The second end of the hose 94 is coupled to a first end ofthe valve 95 that can be controlled by hand or electronically tomaintain a constant flow rate from the hydraulic device 91. A second endof the valve 95 is coupled to communicate with the hydraulic pump 96,that can be hand- or electronically-actuated to drive hydraulic fluidcontained in a reservoir within the pump 96, into the hydraulic device91 via the valve 95, hose 94, and conduit 92.

FIG. 3 is a diagram of an electric power generator 66 preferred for usein the apparatus 1 of this invention. The generator 66 is electricallycoupled to the conductor 62, and also has certain components defined byor situated in contact with the conductor 62, that are cooled bycirculation of the coolant through the generator 66. The generator 66includes an oscillator tube 100 that has a cathode terminal CAT, a gridterminal G and a plate terminal P. The cathode terminal CAT is coupledto receive an a.c. voltage from terminals W and X. The a.c. voltagereceived at terminals W and X heats the cathode terminal CAT to generatefree electrons. The capacitor C1, coupled between the terminal W andground, stabilizes the a.c. voltage applied to the cathode terminal CAT.A terminal Y receives an a.c. signal used to generate oscillations inthe generator 66. More specifically, the capacitors C1, C2, theinductors L1, L2 and the resistors R1-R5 generate oscillations based onthe a.c. signal at the terminal Y, that are applied to the grid terminalG of the oscillator tube 100. The capacitor C2 has a first end coupledto the terminal Y, and a second end coupled to ground. To the terminalY, the first ends of the resistors R1-R4 are coupled. The second ends ofthe resistors R1-R4 are coupled to a capacitor C3 whose opposite end iscoupled to ground. The second ends of the resistors R1-R4 are coupled toa first end of the series combination of the inductor LI and theresistor R5, that have a second end coupled to the grid terminal G and afirst end of a fuse F. The opposite end of the fuse F is coupled to theinductor L2 whose opposite end is coupled to ground. The inductor L2 isvariable to adjust the oscillation frequency of the voltage applied tothe grid terminal G. To urge the electrons from the cathode terminal CATto the plate terminal P, a relatively large d.c. voltage can be appliedto terminal Z of the generator 66. The flow of electrons from thecathode terminal CAT to the plate terminal P depends on the oscillatingsignal at the grid terminal G. The plate terminal P thus generates apowerful a.c. signal that is an amplified version of the a.c. signal atthe grid terminal G. To prevent the plate terminal P from overheating,the coolant from the conductor 62 is supplied to the plate terminal P.The plate terminal P is electrically coupled to an inductor L3 whoseopposite end is coupled to receive the d.c. voltage from the terminal Z.A capacitor C4 is coupled between the terminal Z and ground to stabilizethe d.c. voltage applied to the plate terminal P. A capacitor C5 has afirst end coupled to the terminal Z, and a second end coupled to thefirst ends of the parallel capacitors C6-C9 whose opposite ends arecoupled to ground. The second end of the capacitor C5 is also coupled toa first end of the inductor L4 whose opposite end is coupled to theheating element 60. The capacitors C5-C9 and the inductor L4 arevariable to allow matching of the impedance of the generator 66 with theimpedance associated with the heating element 60 that can vary dependingupon the amount of the charge material 25 in the enclosure 32 of thecooling unit 23. The inductor L4 defined by the conductor 62 receivesthe coolant flow from the coolant supply unit 70 to ensure that theinductor L4 will not overheat. Although the above-described generator 66is preferred for use with the apparatus 1 of this invention, it ispresented by way of example, and not limitation, as many differentgenerators can be used with the apparatus of this invention as will bereadily understood by those of ordinary skill in this field.

FIG. 4 is a relatively detailed cross-sectional view of a preferredembodiment of the feedthrough 64 in accordance with this invention. Theconductor 62 is situated at the core of the feedthrough 64, and isenclosed by a relatively large-diameter portion 101 of the conductor 63.Preferably, the portion 101 is cylindrical in shape, composed of anelongated metal tube made of copper, for example, to establish goodelectrical contact between the outer surface of the portion 101 and aninner surface of the plate member 5 that defines the aperture throughwhich the feedthrough 64 extends. For durability, the metal tubecomposing the portion 101 is preferably relatively thick, for example,about one-half inch thick in radial thickness.

If the coolant flowing in the feedthrough 64 is not electricallyinsulative, electrical insulation should be provided between theconductors 62, 63. To provide electrical insulation between theconductors 62, 63, an electrical insulator 102, preferably with anelongated tube shape, receives the conductor 62 in its hollow interior.The insulator 102 can be composed of an electrically-insulative plasticor ceramic material that is electrically-insulative. Preferably, theportion 101 defines constrictions 103 at its two ends. The constrictions103 are sized so that the insulator 102 securely fits in and issupported by the portion 101. To seal the ends of the portion 101,fittings 104, 105 are disposed at respective ends of the portion 101.The fittings 104, 105 have respective members 106, 107 with centrallydefined apertures, to allow passage of the insulator 102. The members106, 107 have respective relatively large-diameter threaded ends thatare screwed into corresponding threads defined inside of the ends of theportion 101. The members 106, 107, when screwed into the respective endsof the portion 101, form pressure-tight seals used to contain thecoolant flowing in the feedthrough 64. The opposite, relativelysmall-diameter threaded ends of the members 106, 107 receive respectiveapertured caps 108, 109 through the open centers of which extend theinsulator 102. The caps 108, 109 are threaded onto respective ends ofthe members 106, 107 to cause the members 106, 107 to constrict orcompress down upon the insulator 102, to fix the insulator 102 inposition relative to the portion 101. The insulator 102 has a collar 110with a relatively large diameter compared to the other portions of theinsulator 102. The collar 110 abuts the cap 108 to prevent the insulatorfrom sliding toward the right in FIG. 4 relative to the portion 101. Afitting 111 is disposed in contact with the end of the insulator 102,that is situated inside of the vessel 2 during operation of theapparatus 1. The fitting 111 includes a member 112 with relativelylarge-and small-diameter threaded ends. The large-diameter end of thefitting 111 defines a cylindrical recess at one end to receive the endof the insulator 102. A cap 113 with a central aperture through whichthe insulator 102 extends, is disposed between the collar 110 and themember 112, and is screwed into engagement with the large-diameter endof the member 112 to compress the member 112 to grip the insulator 102.The member 112 defines a central aperture that communicates with thecylindrical recess of the member 112, and through which extends theconductor 62. The central aperture is also defined through thesmall-diameter threaded end of the member 112. To the member 112, a cap114 is threaded to compress the member 112 into contact with the outsideof the conductor 62 to fix its position with respect to the insulator102. The cap 114 defines a central aperture through which extends theconductor 62. With the fitting 111 fixed in position relative to theconductor 62, the cap 113 abuts the collar 110 from the side oppositethe cap 108, so that the collar 110 prevents the insulator 102 fromsliding in the portion 101 either to the right or left in FIG. 4.

On the extreme right of the feedthrough 64 in FIG. 4, a fitting 115functions to fix the conductor 62 in position relative to the insulator102. The fitting 115 is similar to the fitting 111, and includes amember 116 that defines a cylindrical recess proportioned to snuglyreceive the end of the insulator 102. A cap 117 of the fitting 115, hasan aperture through which the insulator 102 extends. When screwed ontothe relatively large-diameter threaded end of the member 116, the cap117 compresses the member 116 to engage with and grip the end of theinsulator 102. At the opposite end of the member 116, a small-diameterthreaded end is disposed. The conductor 62 passes through a centralaperture defined in the member 116, that communicates with thecylindrical recess. A cap 118 with a central aperture through which theconductor 62 passes, is screwed onto the small-diameter threaded end ofthe member 116 to cause it to grip and hold the conductor 62 in positionrelative to the insulator 102.

To channel coolant into the hollow interior of the portion 101 betweenthe inside wall of the portion 101 and the outside wall of the insulator102, an arm 120 of the conductor 63, preferably a bent copper tube, hasan end that is coupled by welding, for example, to communicate with thehollow interior of the portion 101 at a position that is outside of thepressure vessel 2 when assembled. On the left side of FIG. 4, an arm 121of the conductor 63, preferably also formed of a bent copper tube, ismounted by welding, for example, to communicate with the hollow interiorof the portion 101, and serves to couple the electric power and coolantflow to the heating element 60. In the preferred embodiment, the fitting65 serves to fix the feedthrough 64 relative to the plate member 5. Thefitting 65 includes a member 122 with a relatively large diameter endthat is threaded into corresponding threads of the plate member 5. Anapertured cap 123 through the open center of which passes the portion101, is screwed onto a relatively small-diameter end of the member 122to compress the member 122 into contact with the portion 101. Thefitting 65 also forms a pressure-tight seal between the plate member 5and the feedthrough 64. Preferably, the other fittings 11, 38, 39, 93 ofthe apparatus 1 are similar in configuration to the fitting 65.

In operation, if the pressure vessel 2 is not already opened, the bolts7 and nuts 8 are loosened and removed from the flanges 4, 6 of thechamber member 2 and the plate member 5, respectively, and the chambermember 2 and the plate member 5 are separated. The chamber member 2 andthe plate member 5, made of the preferred thick steel material, can beextremely heavy so that a steel frame with one or more hydraulic pistons(not shown) can be used to selectively separate or join the chambermember 3 and the plate member 5. The frame preferably bounds the spacein which the pressure vessel 2 is situated, and supports one end of thehydraulic piston(s) while the other end of the piston(s) is coupled toeither the chamber member 3 or the plate member 5, to lift or lower onemember 3, 5 relative to the other member.

The charge material 25, preferably in powdered form, is inserted intothe enclosure 32 defined in the cooling unit 23. With some kinds ofcharge materials 25, susceptor materials are used to raise thetemperature of the charge material 25 to a temperature sufficiently highthat it becomes electrically conductive and thus susceptible to theelectromagnetic field generated by the heating element 60. For example,for silicon carbide (SiC) or yttrium barium cupric oxide (YBa₂ Cu₃O_(x)), pieces of graphite can be inserted into the charge material 25for use as the susceptor material. For aluminum nitride (AlN) oraluminum gallium nitride (AlGaN_(x)), pieces of aluminum can be insertedinto the charge material for use as the susceptor. Also, for aluminumgallium nitride (AlGaN_(x)) and for gallium nitride (GaN), gallium canbe used as the susceptor material. Other material such as tungsten canbe used as susceptor material for suitable types of substances for usein making a crystal from such substances. With some types of chargematerial, beneficial results are obtained by pre-pressing the chargematerial to obtain a compacted mass situated in the enclosure 32 of thecooling unit 23. After situating the charge material 25 and insertingthe appropriate susceptor material, if used, in the enclosure 32, thepressure vessel 2 is enclosed by joining the flange 4 of the chambermember 3 to the flange 6 of the plate member 5 with the gasket 9situated therebetween to form a pressure-tight seal, and by securing theflanges 4, 6 with the bolts 7 and the nuts 8.

The valves 15, 16 of the four-way conduit 13, are closed, and the vacuumunit 18 is activated. The valve 14 of the four-way conduit 13, is openedso that the vacuum unit 18 draws out the atmospheric gases in the spaceenclosed by the pressure vessel 2. After the pressure vessel 2 issufficiently evacuated, the valve 14 is closed and the vacuum unit 16can be deactivated if desired.

In the pressurized gas unit 20, a pressurized gas tank. 21 with theappropriate type of gas to supply the necessary pressure to prevent theperitectic charge material 25 from decomposing, is coupled to the valve22. The selection of the gas type used to supply the pressure to preventperitectic decomposition is generally determined by the compound orelement of the charge material 25 that tends to volatize first after thematerial melts. For example, for yttrium barium cupric oxide (YBa₂ Cu₃O_(x)), oxygen can be used to supply the pressure to prevent peritecticdecomposition of the charge material 25. For aluminum nitride (AIN),gallium nitride (GaN) and aluminum gallium nitride (AlGaN_(x)) chargematerials, nitrogen is an appropriate gas for supplying the pressure toprevent decomposition. However, for some charge materials, gasesunrelated to the charge material composition can be used. For example,for silicon carbide (SiC), nitrogen can be used to supply the pressureneeded to render the silicon carbide congruently-melting to prevent itsperitectic decomposition. Also, for AIN, GaN and AlGaN_(x), an inert gascan be used to supply the pressure need to prevent decomposition.Further, for reducing environments, hydrogen or a hydrogen-inert gasmixture can be used to supply the pressure needed to prevent peritecticdecomposition.

The valve 22 is set to a pressure value appropriate to maintain adesired pressure for the substance composing the charge material 25, toprevent peritectic decomposition. In general, the pressure value neededto prevent peritectic decomposition of the material 25 does not need tobe determined with exactitude. Instead, the pressure value can be set toan arbitrarily high value well above the congruent melting pressurerequired to prevent peritectic decomposition. Alternatively, thepressure value can be determined without undue experimentation for aparticular substance by growing a crystal 26 under a noted pressurevalue, and determining whether the crystal 26 is stoichiometric bycomparing the physical characteristics (for example, conductivity,resistivity, band gap, etc.) of the crystal produced from the chargematerial 25, with known values of such properties for stoichiometriccrystals, and using any difference between the determined and knownvalues of the physical characteristics as a basis to adjust the pressurefor a subsequent iteration of growing a crystal with the apparatus 1.Through successive iterations, at least an approximate value for the gaspressure needed to prevent peritectic behavior of a particular chargematerial can be determined with reasonable precision. In general, it ispreferred to operate at a level sufficiently high above the congruentmelting pressure for a given temperature to ensure that peritecticbehavior will not occur, and yet sufficiently low that significantunnecessary reinforcing material is not required to be added to thepressure vessel.

With the valve 22 set to the appropriate value to provide the necessarypressure to prevent the charge material from decomposing, the valve 15is opened to release as contained in the tank 21. The released gas flowsthrough the valve 22, hose 19, four-way conduit 13, hose 12 and conduit10 to enter the vessel 2 to pressurize the charge material 25 containedin the cooling unit 23 to prevent its decomposition.

To prepare for the crystal-growth mode of operation of the apparatus,the actuator 90 is activated to move the cooling unit 23 to a first,elevated position in FIG. 1, relative to the heating element 60. Thisaction is accomplished by activating the hydraulic pump 96, either byhand or by an electronic control signal, to force hydraulic fluidthrough valve 95, hose 94, conduit 92 and into hydraulic device 91 tocause the hydraulic device 91 to extend.

The coolant pump 49 of the coolant supply unit 42 is activated tocirculate the coolant through the cooling unit 23. Specifically, thecoolant pump 49 drives coolant through the hose 50, the diverter 51, thehose 40, the conduit 36, the flexible conduit 34, the input passagesdefined inside of the manifold 29, where the flow is divided through theindividual elongated members 31, that return the coolant flow to theoutput passages of the manifold 29. The surfaces of the enclosure 32defined by the cooling unit 23 are thus cooled. The coolant flow isforced from the output passages of the manifold 29 through the flexibleconduit 35, the conduit 37, and the hose 41, to return to the coolantsupply unit 42. The orifice 43 builds pressure behind it so that thecoolant will not vaporize in the cooling unit 23 under the severetemperatures generated by the heating element 60. From the orifice 43,the coolant travels to the diverter 44 that couples the flow to the hose45 for supply to the tank 47. The refrigeration unit 53 is activated tocool and drive the coolant 57 through the hose 54, the coil 55, and thehose 56 for return to the unit 53. The coolant 57 flowing in the coil 55transfers heat away from the coolant 48. The coolant 48 is thus cooledand flows to the coolant pump 49 for recirculation.

In the coolant supply unit 70, the coolant pump 76 is activated to forcethe circulation of coolant 75 through the feedthrough 64, the heatingelement 60 and the electric power generator 66. More specifically, thecoolant pump 76 forces the coolant 75 through the hose 77, the diverter78 and into the conduit defined by the conductor 63. The coolant 75further flows through the feedthrough 64, through the heating element 60and into the conduit defined by the conductor 62. The conduit defined bythe conductor 62 passes through the inductor L4 and in proximity to theplate terminal P of the generator's oscillator tube 100, to cool theinductor L4 and the plate terminal P. The pump 76 further forces thecoolant 75 to return to the coolant supply unit 70 via the conduitdefined by the conductor 62. In the coolant supply unit 70, the coolant75 flows through the diverter 71, the hose 72 and into the tank 74. Therefrigeration unit 80 is activated to cool and circulate the coolant 84through the hose 81, the coil 82 and back to the unit 80 via the hose83. The coolant 84 acts to carry heat away from the coolant 75. Thecoolant 75, thus reduced in temperature, returns to the coolant pump 76for recirculation.

The electric power generator 66 is activated to generate a high-powerelectromagnetic field through induction in the coil 61 via conductors62, 63. Particularly at rf frequencies, the shield 85 significantlyhelps to focus the energy emitted radially outward from the coil 61 backto the charge material 25 for use in heating the charge material. Theshield 85 thus provides a significant reduction in the amount of powerrequired by the apparatus 1 during operation. The susceptor material, ifused, will heat and in turn cause the charge material 25 to heatsignificantly, attaining temperatures as high as 2000-4000 Celsius. Atthese high temperatures, the charge material 25, even if notparticularly electrically conductive at room temperature, becomessufficiently conductive to be further heated by the coil 61. However,the cooling action of the cooled surfaces of the enclosure 32 defined inthe cooling unit 23, prevents the exterior portion 24 of the chargematerial 25 from melting. The cooling action of the surface 30 and themembers 31 is not sufficiently great to prevent the interior portion 27of the charge material 25 from becoming molten in the limited areaencircled by the coil 61. The exterior portion 24 thus acts as a skullcrucible that contains the molten interior portion 27 of the chargematerial 25.

Once the interior portion 27 of the charge material becomes molten to asufficient extent, the valve 95 of the actuator 90 is set to anappropriate hydraulic fluid flow rate that is proportional to thedesired rate of crystal growth, and the hydraulic pump 96 is deactivatedto allow fluid to flow out of the hydraulic device 91, the conduit 92,the hose 94, the valve 95 to the reservoir of the hydraulic pump 96,thus initiating the crystal-growth mode of operation. The weight of thecooling unit 23 and the charge material 25 is sufficient to force thehydraulic fluid into the hydraulic pump's reservoir, so that the coolingunit moves in the downward vertical direction in FIG. 1, relative to theheating element 60. Preferably, the setting of the valve 95 allows themost rapid relative movement possible between the cooling unit 23 andthe heating element 60, without incurring the risk of producing adefective crystal due, for example, to formation of a non-flat growthface by moving too rapidly. Typically, growth rates of 5 to 30millimeters per hour are possible with the apparatus 1 without incurringan unreasonable risk of producing defects in the crystal grown. As thehydraulic fluid returns to the hydraulic pump 96, the limited area ofcharge material that is heated in the center of the coil 61, moves upthe axis (the vertical axis in FIG. 1) of the charge material 25. As theliquid interior portion 27 thus advances along the vertical axis in FIG.1 with the limited area heated by the coil 61, the molten portion of thecharge material solidifies in a portion of the charge material bodypreviously heated by the coil 61, thus producing an elongated crystal.Because the molten portion 27 of the charge material is subjected to gaspressure in the vessel 2, decomposition by peritectic reaction isprevented so that the crystal is stoichiometric with few dislocations orlattice defects.

Once the hydraulic device 91 moves to a second position corresponding toa retracted state of the device 91, the electric power generator 66 isdeactivated and the charge material 25 and apparatus 1, are allowed tocool. When the apparatus 1 and the charge material 25 are sufficientlycooled, the coolant supply units 42, 70 are deactivated and the valve 15is closed to stop the gas flow from the pressurized gas unit 20. Thevalve 16 of the four-way conduit 13 is opened to bleed the pressurizedgas from the vessel 2. When the pressurized gas is sufficiently bledfrom the vessel 2, the bolts 7 and the nuts 8 are loosened and removedfrom the flanges 4, 6. The chamber 3 and the plate member 5 areseparated by activating the hydraulic means attached to the supportingframe. Once the pressure vessel 2 is sufficiently opened, the crystal 26can be extracted from the enclosure 32 of the cooling unit 23 andthrough the open end of the cooling unit 23. The crystal can then be cutand polished to a desired size or shape. Depending on crystal type, thecrystal can further be cut into wafers or the like used for themanufacture of electronic or optical devices, or fashioned into a shapeappropriate for superconductive materials.

A system in accordance with this invention includes the apparatus 1 asdescribed above, and in addition, includes the charge material 25 fromwhich the crystals are grown from the liquid phase. The apparatus 1 andthe charge material 25 are used as described above.

The apparatus and system of this invention provide several advantagesrelative to conventional crystal-growing devices. With the apparatus andsystem of this invention, a crystal of a substance that undergoes aperitectic reaction at atmospheric pressure can be grown from the liquidphase due to the pressurization of an appropriate gas contained in thepressure vessel, that prevents the substance from peritecticlydecomposing. Therefore, through pressurization, stoichiometry of themolten charge material is carefully maintained so that the crystal grownwith the apparatus has relatively few crystalline lattice defects, andis thus suitable for a wide band gap semiconductor or other uses in theelectronics or optics industry, for example. Additionally, because thecrystal is grown from the liquid phase, the growth of the crystal can beperformed relatively rapidly compared to conventional crystal-growingdevices. Because of the high power consumption needed to melt the chargematerial for crystal growth, the speed at which the crystal can be grownaffects energy costs as well as crystal production rates. The apparatusand system of this invention thus make possible high crystal productionrates at reduced energy consumption and associated expense. Also,because the molten interior of the charge material is composed of thesame substance as the cooled exterior skull portion of the chargematerial, relatively few impurities are introduced into the crystalgrown with the apparatus and system of this invention. Further, theenergy-focusing capability of the shield helps to prevent heating of theexternal surfaces of the vessel, while reducing power consumption byfocusing the energy emitted by the heating element to the chargematerial. The feedthrough also achieves increased energy efficiencyrelative to conventional crystal-growing devices through the coaxialarrangement of its conductors, that are coupled to supply electriccurrent to the heating element. Also, because the feedthrough definestwo conduits for channeling a coolant flow to and from the heatingelement, the feedthrough is cooled effectively so that the externalsurfaces of the pressure vessel in the vicinity of the feedthrough, arenot heated to temperatures that would damage the feedthrough or platemember, a situation that could otherwise cause the pressurized vessel toexplode by sudden release of the pressurized gas contained therein.Further, the cooling unit and shield reduce heating of the wall of thevessel 2 so that the vessel wall does not become weakened and presentthe danger of rupture and explosion under the pressure exerted by thegas contained in the vessel.

A first method in accordance with this invention includes steps ofcontaining a molten liquid portion of a charge material, in a skullcomposed of a solid portion of the charge material, and a step ofpressurizing at least the molten liquid portion of the charge materialwith a gas during the containing step. Preferably, the method alsoincludes a step of cooling the molten liquid portion of the chargematerial to solidify the charge material to form a crystal, during theperformance of the pressurizing step. Advantageously, through the use ofthe pressurizing step, a substance that undergoes a peritectic reactionat atmospheric pressure can be prevented from decomposing during crystalgrowth so that a crystal with proper stoichiometry, and hence relativelyfew crystalline lattice defects, can be grown from the substance fromits liquid phase. Also, because the containing step uses a solid skullcrucible for containment of the molten charge material of the samesubstance as the charge material, relatively few impurities areintroduced to the crystal from the skull crucible. Also, by performingthe preferred cooling step together with the pressurizing step,peritectic decomposition of a charge material is prevented duringcooling. Accordingly, the molten charge material cools to a solidcrystalline form with few lattice defects.

A second method in accordance with this invention includes a step ofheating an interior portion of a charge material body to melt theinterior portion. The second method also includes a step of cooling anexterior portion of the charge material body so that the exteriorportion is in a solid phase and contains the molten interior portion,during the performance of the heating step. The second method furtherincludes a step of pressurizing the charge material body with a gasduring performance of the heating and cooling steps. Preferably, thesecond method also includes a step of cooling the molten interiorportion of the charge material body to form a solid-phase crystal of thecharge material. Also preferred, the heating step can be performed in alimited area along an axis of the charge material body, and the secondmethod can include a step of moving the heat source in a direction alongthe axis of the material body so that a step of cooling of the interiorportion of the charge material body occurs in a portion of the body thatwas previously heated by the heat source as the heat source progressesalong the axis of the charge material body. Preferably, the secondmethod also includes a step of shielding an inductive element used toheat the charge material, to focus the heating in the interior portionof the charge material body.

Advantageously, the heating of the interior portion of the chargematerial body while cooling the exterior portion of the body, provides aliquid phase molten interior portion that is contained by a cooler,solid phase exterior portion of the same charge material. Thus, theexterior portion of the charge material is not a significant source forthe introduction of impurities into the molten interior portion of thecharge material body. The pressurizing step prevents the interiorportion of the charge material from decomposing in a peritectic reactionupon melting so that the second method can be used to manufacturecrystals of substances that undergo peritectic reactions at atmosphericpressure. Further, the step of moving the heat source along the axis ofthe charge material body allows an elongated crystal to be formed sothat relatively large crystals can be produced by the second method. Inaddition, the shielding of the heating element achieves focusing of theheating step toward the interior of the charge material for moreefficient use of the energy consumed in the heating step.

Several modifications of the apparatus, system and methods of thisinvention are possible without departing from the scope of theinvention. For example, the conduit 10, the hoses 12, 17, 19, and thefour-way conduit 13 with valves 14, 15, 16, could be replaced with oneintegrally-formed four-way conduit, hose or the like, as long as theterminal end of the conduit situated inside of the vessel 2 issufficiently durable to withstand the elevated temperature and pressurein vessel 2. Similarly, with respect to the actuator 90, the conduit 92and hose 94 could be implemented as one integral conduit, hose or thelike without departing from the scope of this invention. Likewise, ifdesired, the conduit 36 and the hose 40, and the conduit 37 and the hose41, can be implemented as respective integral conduits, hoses or thelike. As an alternative configuration for the feedthrough 64, if theportion 101 is sufficiently thick to withstand the pressure produced inthe pressure vessel 2, the constrictions 103 can be omitted so that theportion 101 be machined more readily, for example, by boring out a solidcylinder. Alternatively, the constriction 103 on the right side of FIG.4 can be omitted to allow the portion 101 to be readily machined, andthe constriction 103 on the left side of FIG. 4 can be left in place toadd reinforcement of the feedthrough 64 at the portion thereof that issituated inside of the pressure vessel 2 during operation of theapparatus, and thus, which is subjected to the high pressure produced inthe vessel 2. Also, a thermal shield 125 such as a plate of ceramicmaterial, could be mounted to the inside wall of the chamber member 3with brackets 126 or the like so that, upon joining the chamber member 3to the plate member 5, the thermal shield 125 is disposed above theheating element 60, the cooling unit 23 and the charge material 25contained therein. The effect of the thermal shield 125 is to reduce theamount of heat propagating from the charge material 25 upward in thevertical direction in FIG. 2A, so that the vertical dimension of thechamber member 3 can be reduced without posing a danger of rupture ofthe upper domed wall of the chamber member 3 in FIG. 2A due to thermalweakening. The reduction in the chamber member's dimension made possiblewith the thermal shield 125 can provide a savings in the amount ofmaterial required to manufacture the chamber member 3. Further, althoughin the disclosed embodiment of the apparatus of this invention, theactuator 90 moves the cooling unit 23 relative to the heating element 60that is stationarily fixed to the member 5, with some modification, itis conceivable to use the actuator 90 to drive the heating element 60relative to the cooling unit 23 that is modified to be fixed in astationary position by attachment to the member 5, for example, relativeto the heating element 60. In this modification of the apparatus,respective sections of the conductors 62, 63 between the feedthrough 64and the heating element 60, are made of a flexible conductive tubing.Rather than being attached to the manifold 29, the upper end of theactuator 90 is attached to the heating element 60, and operates in asimilar manner to the embodiment in which the cooling unit 23 is movedrelative to the stationary heating element 60. In this modification ofthe apparatus, the conduits 34, 35 would no longer need to be flexibleas the cooling unit 23 should be stationary by mounting to a platform orthe like supported by the plate member 5.

The many features and advantages of the present invention are apparentfrom the detailed specification and thus, it is intended by the appendedclaims to cover all such features and advantages of the describedapparatus, system and methods which follow in the true spirit and scopeof the invention. Further, since numerous modifications and changes willreadily occur to those of ordinary skill in the art, it is not desiredto limit the invention to the exact construction and operationillustrated and described. Accordingly, all suitable modifications andequivalents may be resorted to as falling within the spirit and scope ofthe invention.

We claim:
 1. An apparatus for growing a crystal from a charge material,the apparatus comprising:a pressure vessel for containing a pressurizedgas; a cooling unit for situation in the pressure vessel, having cooledsurfaces defining an enclosure to receive the charge material, theenclosure being partially opened to expose the charge material topressure exerted by the gas contained in the pressure vessel; aninduction heating element for situation in the pressure vessels forheating an interior portion of the charge material to form a melt zonethat is contained by a relatively cool, exterior portion of the chargematerial that is closer relative to the melt zone, to the cooledsurfaces of the cooling unit; and a shield situated in the pressurevessel in operation of the apparatus, and arranged between the inductionheating element and a wall of the pressure vessel, the shield preventingradio-frequency (rf) radiation generated by the induction heatingelement from significantly heating the pressure vessel's wall.
 2. Anapparatus as claimed in claim 1, further comprising:a pressurized gasunit coupled to communicate with a space enclosed by the pressurevessel, for supplying the pressurized gas to the pressure vessel.
 3. Anapparatus as claimed in claim 2, further comprising:a conduit extendingthrough a wall of the pressure vessel, having a first end communicatingwith the space enclosed by the inside of the pressure vessel and asecond end situated outside of the pressure vessel; a fitting coupled toform a pressure-tight seal between the wall and the conduit; and a valvecoupled between the second end of the conduit and the pressurized gasunit, the valve controlling an amount of pressure of the gas to apreselected value.
 4. An apparatus as claimed in claim 3, furthercomprising:a four-way conduit having first, second and third valvedlegs, and a fourth leg coupled to the second end of the conduit; and avacuum unit coupled to the first valved leg; the pressurized gas unitcoupled to the second valved leg of the four-way conduit, and the firstvalved leg being opened and the second and third valved legs beingclosed to evacuate the pressure vessel with the vacuum unit, the firstand third valved legs being closed and the second valved leg beingopened to supply the pressurized gas to the pressure vessel from thepressurized gas source, and the third valved leg being opened and thefirst and second valved legs being closed to bleed gas from the pressurevessel.
 5. An apparatus as claimed in claim 1, further comprising:aliquid coolant; a first conduit extending through a wall of the pressurevessel, the first conduit having first and second ends, the first end ofthe first conduit situated in the pressure vessel and coupled to supplycoolant to the cooling unit to generate the cooled surfaces of theenclosure of the cooling unit; a first fitting coupled to form apressure-tight seal between the first conduit and the wall; a secondconduit extending through the wall of the pressure vessel, the secondconduit having first and second ends, the first end situated inside ofthe pressure vessel and coupled to the cooling unit to discharge thecoolant from the cooling unit; a second fitting coupled to form apressure-tight seal between the second conduit and the wall; an orificecoupled to communicate with the second conduit, for building up thepressure of the coolant flowing in the cooling unit; a tank receivingthe coolant flow from the orifice; a refrigeration unit coupled to coolthe coolant; and a pump situated outside of the pressure vessel andcoupled to drive the coolant to the second end of the first conduit andto receive the coolant from the tank, for circulating the coolantthrough the cooling unit.
 6. An apparatus as claimed in claim 5, whereinthe cooling unit includesa manifold defining input and output passagescoupled to the first and second conduits, respectively, to receive andexpel the coolant flow from the cooling unit; and a plurality ofelongated cooling members that are circularly arranged to define theinner side cooling surfaces of the enclosure, the elongated coolingmembers having input and output conduits defined by coaxial tubes, thecooling members being mounted to the manifold so that the input andoutput conduits of the cooling members communicate with the input andoutput passages, respectively, of the manifold, the cooled surfaces ofthe cooling members that face inwardly toward a center axis of thecircular arrangement of the cooling members and a surface of themanifold together defining the enclosure.
 7. An apparatus as claimed inclaim 6, further comprising:a protective cylinder fitted in sleeve-likefashion outside of the elongated cooling members, for containing thecharge material.
 8. An apparatus as claimed in claim 1, furthercomprising:a feedthrough extending through a wall of the pressurevessel, and having a first end situated inside of the pressure vessel,coupled to the heating element, and a second end opposite the first end,situated outside of the pressure vessel; and a coolant supply unitcoupled to the feedthrough to circulate the coolant through theinductive heating element.
 9. An apparatus as claimed in claim 8,further comprising:a fitting coupled to form a pressure-tight sealbetween the feedthrough and the wall of the pressure vessel.
 10. Anapparatus as claimed in claim 8, further comprising:an electric powergenerator situated outside of the pressure vessel and coupled to thefeedthrough, generating an alternating current that is supplied to theinductive heating element to heat the interior portion of the chargematerial.
 11. An apparatus as claimed in claim 1, wherein the apparatusreceives a coolant flow and electric power, the apparatus furthercomprising:a feedthrough extending through a wall of the pressurevessel, the feedthrough includinga first elongated electric conductorhaving an inner wall defining a conduit for channeling the coolant flow,and a second elongated electric conductor enclosing a portion of thefirst conductor in a region in which the feedthrough extends through thewall, the second conductor having an inner wall that is spaced from anouter wall of the first conductor to define a conduit for channeling thecoolant flow between the inner wall of the second conductor and theouter wall of the first conductor, the first and second electricconductors having respective first ends coupled inside of the pressurevessel to respective terminals of the heating element, to supply theelectric power to the heating element, and coupled to supply the coolantflow to the heating element through one of the first and secondconduits, and to receive the return coolant flow from the heatingelement through the other of the first and second conduits, and thefirst and second electric conductors having second ends coupled outsideof the pressure vessel to receive the electric power, and coupled sothat the one of the first and second conduits receives the coolant flowfor supply to the heating element, and the other of the first and secondconduits outputs the coolant flow from the heating element.
 12. Anapparatus as claimed in claim 11, further comprising:an electricalinsulator surrounding and contacting the first conductor, to provideelectrical insulation between the first and second conductors, an outerwall of the electrical insulator and the inner wall of the secondconductor defining the channel between the outer wall of the firstconductor and the inner wall of the second conductor.
 13. An apparatusas claimed in claim 1, wherein the heating element includes a coilencircling a longitudinal axis of the cooling unit.
 14. An apparatus asclaimed in claim 1, further comprising;a support member situated in thepressure vessel and supporting the shield in a position to surround theheating element.
 15. An apparatus as claimed in claim 1, furthercomprising:at least one bracket mounted to an inside wall of thepressure vessel, the bracket attached to the shield to support theshield.
 16. An apparatus as claimed in claim 1, wherein the heatingelement encircles the cooling unit in a limited region along an axis ofthe cooling unit, the apparatus further comprising:an actuator situatedin the pressure vessel and coupled to one of the heating element and thecooling unit, and an inner wall of the enclosure, for moving the coolingunit relative to the heating element along the axis so that the meltzone traverses the charge material to form the crystal of the chargematerial that extends along the axis.
 17. An apparatus as claimed inclaim 16, wherein the actuator includesa hydraulic fluid; a hydraulicdevice situated inside of the pressure vessel, mechanically coupledbetween one of the heating element and the cooling unit, and the innerwall of the pressure vessel, for moving the heating element relative tothe cooling unit, based on a flow of the hydraulic fluid, a hydraulicpump situated outside of the pressure vessel, and a valve situatedoutside of the pressure vessel and coupled to receive hydraulic fluidflowing between the device and the pump, the actuator having apreparatory mode of operation in which the pump is actuated to force thehydraulic fluid to move the cooling unit to a first position relative tothe heating element, and the actuator having a crystal-growing mode ofoperation in which the weight of the one of the cooling unit and theheating element, drives the hydraulic fluid out of the device and intothe pump at a preselected constant flow rate determined by the valve, sothat the cooling unit moves from the first position to a second positionrelative to the heating element, to form a crystal of the chargematerial extending between the first and second positions.
 18. Anapparatus as claimed in claim 1, wherein the pressure vessel includesachamber member having an open end, and a flange adjacent the open end, aplate member having a flange, supporting the heating element and thecooling unit, a gasket situated between the chamber member and the platemember, and a plurality of bolts for securing the flange of the chambermember to the flange of the plate member so that the open end of thechamber member is enclosed by the plate member and so that the gasketforms a pressure-tight seal between the flanges of the chamber and platemembers.
 19. An apparatus as claimed in claim 1, further comprising:athermal shield supported by the pressure vessel and situated between theheating element and a wall of the pressure vessel, to impede heating ofthe wall of the pressure vessel.
 20. A system receiving a pressurizedgas, the system comprising:a pressure vessel for containing thepressurized gas; a cooling unit situated in the pressure vessel, havingcooled surfaces defining an enclosure with at least one opening; acharge material positioned inside of the enclosure of the cooling unitand exposed through the opening of the enclosure to pressure exerted bythe gas contained in the pressure vessel; an induction heating elementsituated in the pressure vessel, for heating an interior portion of thecharge material to form a melt zone that is contained by a relativelycool, exterior portion of the charge material that is closer relative tothe melt zone, to the cooled surfaces of the cooling unit; and a shieldarranged between the heating element and a wall of the pressure vesselthe shield preventing radio-frequency (rf) radiation generated by theinduction heating element from significantly heating the pressurevessel's wall.
 21. A system as claimed in claim 20, wherein the chargematerial includes at least one of GaN, AlN, SiC, YBa₂ Cu₃ O_(x) andAlGaN_(x).
 22. A system as claimed in claim 20, wherein the chargematerial is composed of a substance that undergoes a peritectic reactionat atmospheric pressure.
 23. A system as claimed in claim 20, whereinthe charge material includes susceptor material to facilitate melting ofthe interior portion of the charge material.
 24. A method comprising thesteps of:a) containing a molten liquid portion of a charge material, ina skull composed of a solid portion of the charge material; and b)pressurizing at least the molten liquid portion of the charge materialwith a gas at a pressure in excess of one-hundred atmospheres, duringthe performance of the step (a).
 25. A method as claimed in claim 24,further comprising the step of:c) cooling the molten liquid portion ofthe charge material to solidify the charge material to form a crystal,during the performance of the step (b) of pressurizing.
 26. A methodcomprising the steps of:a) heating an interior portion of a chargematerial body to melt the interior portion with radio-frequency (rf)radiation; b) during performance of the step (a), cooling an exteriorportion of the charge material body so that the exterior portion is in asolid phase and contains the molten interior portion; c) pressurizingthe charge material body in a pressure vessel with a gas duringperformance of the steps (a) and (b), and d) shielding the pressurevessel from the rf radiation generated in the step (a).
 27. A method asclaimed in claim 26, further comprising the step of:d) cooling themolten interior portion of the charge material body to form asolid-phase crystal of the charge material.
 28. A method as claimed inclaim 27, wherein the step (a) of heating the charge material body isperformed by a heat source in a limited area along an axis of the chargematerial body, the method further comprising the step of:e) moving theheat source relative to the material body, along the axis of thematerial body, the step (d) of cooling the interior portion of thecharge material body occurring along the axis of the charge materialbody in a region of the material body previously heated by the limitedheated area as the heat source moves along the axis of the chargematerial body.
 29. A method as claimed in claim 28, wherein said step(e) is performed at a rate of at least one millimeter per hour.
 30. Amethod as claimed in claim 26, whereinthe shielding in the step (d) isperformed so as to direct the rf radiation to the charge material body.31. An apparatus as claimed in claim 1, wherein the shield reflects atleast some rf radiation away from the pressure vessel's wall.
 32. Anapparatus as claimed in claim 1, wherein the shield reflects at leastsome of the rf radiation toward the charge material contained in thecooling unit.
 33. An apparatus as claimed in claim 1, wherein the shieldis electrically conductive.
 34. An apparatus as claimed in claim 33,wherein the shield is electrically coupled to an end of the heatingelement.
 35. An apparatus as claimed in claim 34, wherein one end of theheating element is electrically grounded.
 36. An apparatus as claimed inclaim 1, wherein the shield has a cylindrical wall that surrounds theheating element.
 37. An apparatus as claimed in claim 1, wherein theshield is formed of metal.
 38. An apparatus as claimed in claim 37,wherein the metal includes copper.
 39. A method as claimed in claim 24,wherein said step (b) is performed above one-hundred-and-fiftyatmospheres of pressure.
 40. A method as claimed in claim 26, whereinsaid step (c) is performed above one-hundred atmospheres of pressure.41. A method as claimed in claim 26, wherein said step (c) is performedabove one-hundred-and-fifty atmospheres.
 42. A method as claimed inclaim 26, wherein the shielding of said step (d) is performed so as todirect at least some radiation toward the charge material body.
 43. Anapparatus for growing a crystal from a charge material, the apparatuscoupled to receive electric power and coolant, the apparatuscomprising:a pressure vessel for containing a pressurized gas; a coolingunit for situation in the pressure vessel, having cooled surfacesdefining an enclosure to receive the charge material; an inductionheating element for situation in the pressure vessel, for heating aninterior portion of the charge material to form a melt zone that iscontained by a relatively cool, exterior portion of the charge materialthat is closer relative to the melt zone, to the cooled surfaces of thecooling unit, the heating element defining a conduit having two oppositeterminal ends through which the coolant passes; and a feedthroughextending through a wall of the pressure vessel, and having a first endsituated inside of the pressure vessel, that is coupled to the heatingelement, and a second end opposite the first end, situated outside ofthe pressure vessel, the feedthrough having first and second conductorsthat are coaxial at least in a portion of the feedthrough that extendsthrough the pressure vessel wall, the first and second conductors of thefeedthrough coupled to respective ends of the heating element to supplythe electric power to the heating element and to circulate the coolantthrough the heating element.
 44. An apparatus as claimed in claim 43,further comprising:a fitting coupled to form a pressure-tight sealbetween the feedthrough and the wall of the pressure vessel.
 45. Anapparatus as claimed in claim 43, wherein the seal formed by the fittingcan withstand a pressure above one-hundred atmospheres.
 46. An apparatusas claimed in claim 43, wherein the seal formed by the fitting canwithstand a pressure above one-hundred-and-fifty atmospheres.
 47. Anapparatus as claimed in claim 43, further comprising:a coolant supplyunit coupled to circulate the coolant through the inductive heatingelement.
 48. An apparatus as claimed in claim 43, further comprising:anelectrical insulator surrounding and contacting the first conductor, toprovide electrical insulation between the first and second conductors,an outer wall of the electrical insulator and the inner wall of thesecond conductor defining the channel between the outer wall of thefirst conductor and the inner wall of the second conductor.